Illumination system

ABSTRACT

An illumination system includes multiple light emitting devices arranged in an area so as to be spaced apart from each other. Each light emitting device includes multiple light emitting diode arrays each of which has one light emitting diode or a plurality of light emitting diodes connected in series. The numbers of the light emitting diodes included in each light emitting diode arrays differs from each other. A controller is configured to establish one or more groups each including one or more light emitting devices and adjust an illumination state of each light emitting device by controlling the driving state of the one or more light emitting diode arrays included in each light emitting device. The controller may select the number of light emitting devices included in each group based on an external condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. patent application Ser. No. 11/994,308 filed Dec. 28, 2007, which is the National Stage Entry of International Application No. PCT/KR2006/001726, filed on May 9, 2006, and claims priority from and the benefit of Korean Patent Application No. 10-2005-0056175, filed on Jun. 28, 2005; Korean Patent Application No. 10-2005-0104952, filed on Nov. 3, 2005; Korean Patent Application No. 10-2005-0126872, filed on Dec. 21, 2005, Korean Patent Application No. 10-2005-0126873, filed on Dec. 21, 2005, Korean Patent Application No. 10-2005-0126904, filed on Dec. 21, 2005 and Korean Patent Application No. 10-2006-0013322, filed on Feb. 11, 2006, which are all hereby incorporated by reference for all purposes as if fully set forth herein. This application is related to U.S. patent application Ser. No. 12/837,805, filed on Jul. 16, 2010, which is a continuation of U.S. patent application Ser. No. 11/994,308, and U.S. patent application Ser. No. 12/908,692, filed on Oct. 20, 2010, which is a continuation of U.S. patent application Ser. No. 11/994,308.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device, and more particularly, to a light-emitting device for an alternating current (AC) power operation, which has an array of light emitting cells connected in series.

2. Discussion of the Background

A light emitting diode (LED) is an electroluminescence device having a structure in which an N-type semiconductor and a P-type semiconductor are joined together, and emits light through recombination of electrons and holes. Such an LED has been widely used for a display and a backlight. Further, since the LED has less electric power consumption and a longer service life as compared with conventional light bulbs or fluorescent lamps, its application area has expanded to the use thereof for general illumination while substituting the conventional incandescent bulbs and fluorescent lamps.

The LED repeats on/off in accordance with the direction of a current under an AC power source. Thus, if the LED is used while being connected directly to the AC power source, there is a problem in that it does not continuously emit light and is easily damaged by reverse currents.

To solve such a problem of the LED, an LED that can be used while being connected directly to a high voltage AC power source is proposed in International Publication No. WO 2004/023568A1 entitled “LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS” by SAKAI et al.

According to the disclosure of WO 2004/023568A1, LEDs are two-dimensionally connected in series on an insulative substrate such as a sapphire substrate to form LED arrays. Two LED arrays are connected in reverse parallel on the sapphire substrate. As a result, there is provided a single chip light emitting device that can be driven by means of an AC power supply.

FIGS. 1 and 2 are schematic circuit diagrams illustrating a conventional light emitting device having light emitting cells connected in series; FIG. 3 is a schematic graph illustrating a driving voltage and a current with time in the conventional light emitting device; and FIG. 4 is a schematic graph illustrating a driving voltage and a light emission amount of the conventional light emitting device.

Referring to FIGS. 1 and 2, light emitting cells C₁ to C_(n) are connected in series to constitute an array. At least two arrays are provided within a single chip 15 in FIG. 2, and these arrays are connected in reverse parallel to each other. Meanwhile, an AC voltage power source 10 in FIG. 2 is connected to both ends of the arrays. As shown in FIG. 2, an external resistor R1 is connected between the AC power source 10 and the LED 15.

The light emitting cells C₁ to C_(n) of the array are operated for a ½ cycle of the AC voltage power source and the other array connected in reverse parallel to the array is operated for the other ½ cycle thereof. Accordingly, the arrays are alternately operated by means of the AC voltage power source.

However, the light emitting cells connected in series are simultaneously turned on or off by mean of an AC voltage. Thus, when the AC voltage has a value larger than the sum of threshold voltages of the light emitting cells, a current begins to flow through the light emitting cells. That is, the light emitting cells simultaneously begin to be turned on when the AC voltage exceeds the sum of the threshold voltages, and they are simultaneously turned off in a case where the AC voltage is less than the sum of the threshold voltages.

Referring to FIG. 3, before an AC voltage exceeds a predetermined value, the light emitting cells are not turned on and a current does not flow therethrough. Meanwhile, when a certain period of time lapses and the AC voltage exceeds the predetermined value, a current begins to flow through the array of the light emitting cells. Meanwhile, when the time is at T/4 while the AC voltage is more increased, the current has a maximum value and is then decreased. On the other hand, if the AC voltage is less than the predetermined value, the light emitting cells are turned off and a current does not flow therethrough. Thus, a time during which a current flows through the light emitting cells is relatively shorter than T/2.

Referring to FIGS. 4 (a) and (b), the light emitting cells emit light when a predetermined current flows through them. Thus, an effective time during which the light emitting cells are driven to emit light becomes shorter than a time during which a current flows through the light emitting cells.

As the effective time during which light is emitted becomes short, light output is decreased. And thus, a high peak value of a driving voltage may be needed to increase the effective time. However, in this case, power consumption in the external resistor R1 is increased, and a current is also increased according to the increase in the driving voltage. The increase in a current leads to increase in the junction temperature of the light emitting cells, and the increase in the junction temperature reduces the light emitting efficiency of the light emitting cells.

Further, since the light emitting cells are operated only when the voltage of the AC power source exceeds the sum of the threshold voltages of the light emitting cells within the array, the light emitting cells are operated in a rate slower than a phase change rate of the AC power source. Accordingly, uniform light is not continuously emitted on a substrate and a flicker effect occurs. Such a flicker effect remarkably appears when an object moving at a certain distance from a light source is viewed. Even though the effect is not observed with the naked eye, it may cause eye fatigue if the light emitting cells are used for illumination for a long period of time.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light-emitting device for an AC power operation, wherein a flicker effect can be prevented or reduced, and a time during which light is emitted is increased corresponding to a phase change in an AC voltage.

Another object of the present invention is to provide a light emitting device, wherein an operation can be made with a lower current as compared with a prior art, thereby improving light emitting efficiency.

To achieve these objects, the present invention provides a light-emitting device for an AC power operation, the device having an array of light emitting cells connected in series. An aspect of the present invention provides a light emitting device, wherein light emitting cells within arrays are sequentially turned on and off. The light emitting device according to the aspect of the present invention comprises a light emitting diode (LED) chip having an array of light emitting cells connected in series; and switching blocks respectively connected to nodes between the light emitting cells. The light emitting cells are sequentially turned on and off by the switching blocks when the array is connected to and driven by an AC voltage power source. Since the light emitting cells are sequentially turned on and off, an effective time during which the light emitting cells emit light can be increased as whole.

The switching blocks may be connected to source and ground terminals of the array. At this time, an n-th switching block may short the ground terminal and a node to which the n-th switching block is connected when a voltage difference V_(ac) between the source and ground terminals is in a range of (Predetermined Voltage×n) to (Predetermined Voltage×(n+1)), and may open the node from the ground terminal if the voltage difference V_(ac) is greater than (Predetermined Voltage×(n+1)). Accordingly, when an AC voltage is increased, the switching blocks sequentially repeat the short-circuiting and the opening so that the light emitting cells can be sequentially turned on. When the AC voltage is decreased, the light emitting cells are sequentially turned off.

The predetermined voltage may be a forward voltage of the light emitting cells at a reference current. Accordingly, a current flowing through the light emitting cells can be constantly maintained to be a current approximate to the reference current. Thus, the light emitting efficiency of the light emitting cells can be improved by adjusting the reference current. For example, the reference current may be 15 to 25 mA.

The light emitting cells may be turned off in an order reverse to the order in which the light emitting cells are turned on. Alternatively, they may be turned off in the order in which the light emitting cells are turned on.

Each of the light emitting cells may comprise an N-type semiconductor layer, a P-type semiconductor layer and an active layer interposed therebetween. Further, the semiconductor layers may be made of a GaN based semiconductor.

Meanwhile, the LED chip may further comprise another array of light emitting cells connected in series, in addition to the array of the light emitting cells connected in series. These arrays are connected in reverse parallel to each other. Switching blocks may be connected to nodes of the light emitting cells within the other array of the light emitting cells connected in series, respectively. At this time, the switching blocks connected to nodes of the light emitting cells within the array of the light emitting cells connected in series may be connected to the nodes of the light emitting cells within the other array, respectively.

Another aspect of the present invention provides a light-emitting device for an AC power operation, the device comprising a plurality of arrays that have different numbers of light emitting cells connected in series and are connected in parallel to one another. The AC light-emitting device according to this aspect of the present invention includes a substrate. A plurality of first arrays are positioned on the substrate. The first arrays have the different numbers of light emitting cells connected in series and are connected in reverse parallel to one another. Further, a plurality of second arrays are positioned on the substrate. The second arrays have the different numbers of light emitting cells connected in series and are connected in reverse parallel to the first arrays. Accordingly, it is possible to provide an AC light-emitting device, wherein the arrays are sequentially turned on and then turned off in reverse order under an AC power source so that a flicker effect can be reduced and light emission time can be increased.

In some embodiments, the light emitting device may further comprise a switching block for controlling light emission of each of the plurality of first and second arrays depending on a voltage level of an AC power source. The switching block selectively controls the light emission of the arrays depending on the voltage level of the AC power source. At this time, one terminal of each of the first and second arrays is connected in common to a first power source connection terminal, and the other terminals thereof are connected to second power source connection terminals, respectively. In addition, the switching block may be connected between the second power source connection terminals and the AC power source to form a current path depending on the voltage level of the AC power source, thereby controlling the light emission of the arrays.

In some embodiments, each of the second arrays may have the same number of light emitting cells as each of the corresponding arrays in the first arrays. Thus, it is possible to provide a light emitting device having identical light output and light emitting spectrum according to a phase change in an AC power source. Further, an array having the greater number of the light emitting cells in the first and second arrays may have larger light emitting cells.

In some embodiments, first resistors may be respectively connected in series to the first arrays. Moreover, second resistors may be respectively connected in series to the second arrays. The first and second resistors are employed to prevent an excessive current from flowing into the first and second arrays.

The first resistors may have different resistance values, and the second resistors may also have different resistance values. The first and second resistors may be respectively connected in series to the first and second arrays in such a manner that a resistor with a larger resistance value is connected to an array having the smaller number of the light emitting cells. Accordingly, an excessive current can be prevented from flowing in an array that has been first turned on.

Meanwhile, the second resistors may have resistance values corresponding to those of the first resistors. Accordingly, it is possible to provide a light emitting device having identical light output and light emitting spectrum in relation with a phase change in an AC power source.

Instead of the first and second resistors, a common resistor may be serially connected in common to the first and second arrays. Accordingly, the arrays are sequentially operated due to differences in the numbers of the light emitting cells. Since the common resistor is connected to the respective arrays, a process of connecting a resistor is simplified.

The resistors or common resistor may be positioned on the substrate or outside the substrate. That is, the resistors or common resistor may be formed inside an LED chip, or alternatively may be formed in an additional resistor device that in turn is connected to the arrays.

Meanwhile, in each of the first and second arrays, light emitting cells within an array having the smallest number of the light emitting cells may have luminous intensity larger than that of light emitting cells within an array having the greatest number of the light emitting cells. Accordingly, it is possible to provide an AC light-emitting device, wherein the arrays are sequentially turned on and then turned off in reverse order under an AC power source so that light emission time can be increased, and arrays which are initially turned on have larger luminous intensity so that a flicker effect can be reduced.

The light emitting cells within the array having the smallest number of the light emitting cells may have roughened surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells. The roughened surfaces of the light emitting cells prevent total reflection due to difference in refraction index, thereby improving the extraction efficiency of light emitted to the outside. Accordingly, the luminous intensity of the light emitting cell is increased.

The light emitting cells with the roughened surfaces may constitute arrays of which the number is ½ of the number of the arrays in each of the first and second arrays. In this case, the arrays of the light emitting cells with the roughened surfaces have the relatively smaller number of the light emitting cells. Meanwhile, the arrays of the light emitting cells with the roughened surfaces may be limited to arrays having the smallest number of the light emitting cells in each of the first and second arrays.

Meanwhile, the light emitting cells within the array having the smallest number of the light emitting cells may have inclined side surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells. The inclined side surfaces improve light extraction efficiency to increase the luminous intensity of the light emitting cells.

The light emitting cells with the inclined side surfaces may constitute arrays of which the number is ½ of the number of the arrays in each of the first and second arrays. In this case, the arrays of the light emitting cells with the inclined side surfaces are have the relatively smaller number of the light emitting cells. Meanwhile, the arrays of the light emitting cells with the inclined side surfaces may be limited to arrays having the smallest number of the light emitting cells in each of the first and second arrays.

A further aspect of the present invention provides a light emitting device for an AC power operation, the device comprising a bridge rectifier.

The AC light-emitting device according to this aspect includes a substrate. A plurality of arrays are positioned on the substrate. The plurality of arrays have different numbers of light emitting cells connected in series and are connected in parallel to one another. In addition, a bridge rectifier is connected to the plurality of arrays. Two nodes of the bridge rectifier are connected to both end portions of the arrays, respectively. Accordingly, it is possible to provide an AC light emitting device, wherein the arrays are driven by means of a current rectified by the bridge rectifier, and it is also possible to provide a light emitting device, wherein the arrays are repeatedly turned on in sequence and then turned off in reverse order due to difference in the numbers of the light emitting cells.

The bridge rectifier may be positioned on the substrate. Accordingly, the bridge rectifier may be formed together with the light emitting cells. On the contrary, a bridge rectifier may be separately provided and then connected to the arrays.

In some embodiments, a switching block may be connected between one end portions of the arrays and one of the nodes of the bridge rectifier. The switching block controls light emission of each of the plurality of the arrays depending on a voltage level of an AC power source.

In some embodiments, resistors may be positioned between the bridge rectifier and the plurality of the arrays and connected in series to the plurality of the arrays, respectively. The resistors prevent an excessive current from flowing into the arrays.

The resistors may have different resistance values. At this time, the resistors are respectively connected in series to the plurality of arrays in such a manner that a resistor with a larger resistance value is connected to an array having the smaller number of the light emitting cells. Accordingly, an excessive current can be prevented from flowing in an array that has been first turned on.

Instead of the plurality of resistors, a common resistor may be serially connected in common to the plurality of arrays. If the common resistor is employed, a process of connecting a resistor can be simplified.

Meanwhile, an array having the greater number of the light emitting cells in the plurality of arrays may have larger light emitting cells.

In some embodiments, in the plurality of arrays, light emitting cells within an array having the smallest number of the light emitting cells may have luminous intensity larger than that of light emitting cells within an array having the greatest number of the light emitting cells. For example, the light emitting cells within the array having the smallest number of the light emitting cells may have roughened surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells. Alternatively, the light emitting cells within the array having the smallest number of the light emitting cells may have inclined side surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells.

A still further aspect of the present invention provides an AC light-emitting device comprising a delay phosphor. The AC light-emitting device according to this aspect comprises an LED chip having a plurality of light emitting cells; a transparent member for covering the LED chip; and a delay phosphor excited by light emitted from the light emitting cells to emit light in a visible light range.

Here, the term “delay phosphor” is also referred to as a long afterglow phosphor, and means a phosphor having a long decay time after an excitation light source is blocked. Here, the decay time is defined as a time taken to reach 10% of an initial value after the excitation light source has been blocked. In this embodiment, the delay phosphor may have a decay time of 1 msec or more, preferably about 8 msec or more. Meanwhile, although an upper limit of the decay time of the delay phosphor is not limited to specific values, it may be preferred that it be not too long according to uses of light emitting devices. For example, in case of a light emitting device used for general household illumination, the decay time of the delay phosphor is preferably a few minutes or less. The decay time is sufficiently 10 hours or less even for interior illumination.

According to this embodiment, when an LED chip emits visible light, the light emitted from the LED chip and light emitted from the delay phosphor are mixed to increase the light emission time of the light emitting device, thereby preventing a flicker effect of an AC light-emitting device.

The delay phosphor may be positioned between the LED chip and the transparent member, or dispersed within the transparent member.

The delay phosphor may be one of red, green and blue phosphors, or a combination thereof.

In addition to the delay phosphor, the AC light-emitting device may further comprise another phosphor excited by light emitted from the LED chip to emit light in a visible light range. Such a phosphor is employed to provide light emitting devices capable of emitting light having various colors by converting the wavelength of light emitted from the LED chip. For example, in a case where the LED chip emits ultraviolet light, the other phosphors may be red, green and/or blue phosphors to emit white light through mixing with light in a visible light range emitted from the delay phosphor. Further, in a case where the LED chip emits blue light, the other phosphors may be a red phosphor and/or a green phosphor, or a yellow phosphor.

According to the present invention, it is possible to provide a light emitting device for an AC power operation, wherein a flicker effect can be prevented or reduced and a time during which light is emitted is increased corresponding to a phase change in an AC voltage. Further, it is possible to provide a light emitting device, wherein an operation can be made with a lower current as compared with a prior art, thereby improving light emitting efficiency.

Exemplary embodiments of the present invention also provide an illumination system capable of adjusting an illumination state based on a variation of brightness in an area or a change in a motion of an object in the area. Light emitting devices included in the illumination system may be grouped together and an illumination state of each light emitting device of a group can be adjusted together. Accordingly, a more efficient control of the illumination system may be provided and energy consumption efficiency may be improved.

An exemplary embodiment of the present invention also discloses an illumination system, including: a plurality of light emitting devices arranged in an area and spaced apart from each other, each light emitting device comprising a plurality of light emitting diode arrays each comprising one light emitting diode or a plurality of light emitting diodes connected in series, the numbers of light emitting diodes in each light emitting diode array being different from the number of light emitting diodes in each other light emitting diode array; and a controller configured to establish one or more groups, each group comprising one or more of the light emitting devices, and the controller configured to adjust an illumination state of a selected group of the one or more groups by adjusting the illumination state of each light emitting device in the selected group by controlling a driving state of the light emitting diode arrays included in each light emitting device of the selected group, wherein the controller determines the number of light emitting devices included in each group based on sensing information.

An exemplary embodiment of the present invention also discloses a method of driving a plurality of light emitting devices in an area, the method including: driving a first light emitting diode array of the light emitting devices based on an initial illumination state; receiving sensing information for the area; dividing the area into a plurality of groups, each group comprising at least one light emitting device, based on the received sensing information; and adjusting an illumination state of the light emitting devices in each group in response to the sensing information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are schematic circuit diagrams illustrating a conventional AC light-emitting device.

FIG. 3 is a schematic graph illustrating a driving voltage and a current with time in the conventional AC light-emitting device.

FIG. 4 is a schematic graph illustrating a driving voltage and a light emission amount of the conventional AC light-emitting device.

FIG. 5 is a partial sectional view illustrating an AC light-emitting diode (LED) according to an embodiment of the present invention.

FIG. 6 is a partial sectional view illustrating an AC LED according to another embodiment of the present invention.

FIG. 7 is a schematic circuit diagram illustrating an AC light-emitting device according to a first embodiment of the present invention.

FIG. 8 is a schematic graph illustrating a driving voltage and a current with time in the AC light-emitting device according to the first embodiment of the present invention.

FIG. 9 is a schematic circuit diagram illustrating an AC light-emitting device according to a second embodiment of the present invention.

FIG. 10 is a schematic graph illustrating a driving voltage and a light emission amount of the AC light-emitting device according to the second embodiment of the present invention.

FIG. 11 is a schematic circuit diagram illustrating an AC light-emitting device according to a third embodiment of the present invention.

FIG. 12 is a schematic circuit diagram illustrating a modification of the AC light-emitting device according to the third embodiment of the present invention.

FIG. 13 is a schematic graph illustrating a driving voltage and a light emission amount of the AC light-emitting device according to the third embodiment of the present invention.

FIG. 14 is a schematic circuit diagram illustrating an AC light-emitting device according to a fourth embodiment of the present invention.

FIG. 15 is a schematic circuit diagram illustrating an AC light-emitting device according to a fifth embodiment of the present invention.

FIG. 16 is a schematic circuit diagram illustrating an AC light-emitting device according to a sixth embodiment of the present invention.

FIGS. 17 and 18 are sectional views illustrating LEDs applicable to the embodiments of the present invention.

FIG. 19 is a sectional view illustrating an AC light-emitting device according to a seventh embodiment of the present invention.

FIG. 20 is a schematic graph illustrating a light emitting characteristic of an AC light-emitting device according to the seventh embodiment of the present invention.

FIG. 21 is a diagram of an illumination system according to an exemplary embodiment of the present invention.

FIG. 22 is a diagram illustrating a controller according to an exemplary embodiment of the present invention.

FIG. 23 is a diagram of an illumination adjustment method according to an exemplary embodiment of the present invention.

FIG. 24 is a diagram of a light emitting module according to an exemplary embodiment of the present invention.

FIG. 25 is a diagram of an illumination adjustment method according to an exemplary embodiment of the present invention.

FIG. 26 is a diagram of an illumination adjustment method according to an exemplary embodiment of the present invention.

FIG. 27 is a diagram of an illumination adjustment method according to an exemplary embodiment of the present invention.

FIG. 28 is a diagram of a light emitting module according to an exemplary embodiment of the present invention.

FIG. 29 is a flowchart of an illumination method according to exemplary an embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided only for illustrative purposes so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the following embodiments but may be implemented in other forms. In the drawings, the widths, lengths, thicknesses and the like of elements are exaggerated for convenience of illustration. Like reference numerals indicate like elements throughout the specification and drawings.

It will be understood that when an element or layer is referred to as being “on” or “connected to” another element or layer, it can be directly on or directly connected to the other element or layer, or intervening elements or layers may be present. In contrast, when an element or layer is referred to as being “directly on” or “directly connected to” another element or layer, there are no intervening elements or layers present. It will be understood that for the purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ).

FIG. 5 is a partial sectional view illustrating a light emitting diode (LED) according to an embodiment of the present invention.

Referring to FIG. 5, light emitting cells 30 spaced apart from one another are positioned on a substrate 20. Each of the light emitting cells 30 comprises a first conductive type semiconductor layer 25, a second conductive type semiconductor layer 29 positioned on a region of the first conductive type semiconductor layer 25, and an active layer 27 interposed between the first and second conductive type semiconductor layers. Here, the first and second conductive type semiconductor layers 25 and 29 are of an N-type and a P-type, or a P-type and an N-type, respectively.

An electrode 31 may be formed on the second conductive type semiconductor layer 29. The electrode 31 may be a transparent electrode through which light can be transmitted.

The light emitting cells 30 can be formed by forming the respective semiconductor layers and an electrode layer on the substrate 20 and then patterning them using photolithography and etching processes. The substrate 20 may be a substrate made of Al₂O₃, SiC, ZnO, Si, GaAs, GaP, LiAl₂O₃, BN, AlN or GaN, and selected depending on the material of a semiconductor layer to be formed on the substrate 20. If a GaN based semiconductor layer is formed, the substrate 20 may be an Al₂O₃ or SiC substrate.

A buffer layer 21 may be interposed between the substrate 20 and each of the light emitting cells 30. The buffer layer 21 is a layer for reducing a lattice mismatch between the substrate 20 and subsequent layers in crystal growth. For example, the buffer layer 21 may be a GaN or AlN film. The N-type semiconductor layer is a layer in which electrons are produced and may be formed of GaN doped with N-type impurities. The P-type semiconductor layer is a layer in which holes are produced and may be formed of AlGaN doped with P-type impurities.

The active layer 27 is a region where predetermined band gaps and quantum wells are made so that electrons and holes can be recombined, and may include an Al_(x)In_(y)Ga_(z)N layer. The wavelength of light emitted when the electrons and holes are combined varies depending on a compositional ratio of elements constituting the active layer 27. Thus, a compositional ratio between Al, In and Ga is selected to emit light with a required wavelength, e.g., ultraviolet or blue light.

An electrode pad 33 a may be formed on a region of the first conductive type semiconductor layer 25 and an electrode pad 33 b may be formed on the electrode 31. Each of the electrode pads 33 a and 33 b can be formed at a desired position using a lift-off technique.

Wires 41 electrically connect adjacent light emitting cells 30 to each other to form an array having the light emitting cells 30 connected in series. As shown in this figure, each of the wires 41 connects the electrode pad 33 a formed on the first conductive type semiconductor layer 25 of one light emitting cell to the electrode pad 33 b formed on the electrode 31 of the other light emitting cell. The wires 41 may be formed using an air bridge or step-coverage process.

FIG. 6 is a sectional view illustrating an LED according to another embodiment of the present invention. Since the LED of this embodiment is mostly identical with that of FIG. 5, only a difference will be described.

Referring to FIG. 6, a reflective metal layer 51 is formed on each electrode 31. The reflective metal layer 51 may be formed as a single layer or multiple layers. For example, the reflective metal layer may be made of Ag, and barrier metal layers for preventing diffusion of Ag may be formed on and beneath the reflective metal layer, respectively. The reflective metal layer reflects light generated from the active layer 27 toward the substrate 20. Thus, it is preferred that the substrate 20 be a light transmitting substrate. The electrode pad 33 b may be formed on the reflective metal layer 51, or it may be omitted. Meanwhile, instead of formation of the reflective metal layer 51, the electrode 31 may be formed as a reflective metal layer.

Meanwhile, a metal bumper 53 is formed on the reflective metal layer 51. The metal bumper 53 is bonded on a submount (not shown) to transfer heat generated from a light emitting cell.

According to this embodiment, there may be provided a flip-chip type LED having the metal bumpers 53 thermally contacted with a submount. Such a flip-chip type LED has superior heat-dissipating efficiency and thus provides high light output.

FIG. 7 is a schematic circuit diagram illustrating an AC light-emitting device according to a first embodiment of the present invention, and FIG. 8 is a schematic graph illustrating a driving voltage and a current with time in the AC light-emitting device according to the first embodiment of the present invention.

Referring to FIG. 7, the light emitting device comprises an array of light emitting cells C₁ to C_(n) connected in series. The array is formed on a single LED chip. A plurality of arrays may be formed on a single chip and these arrays are connected in reverse parallel to one another. Accordingly, the light emitting cells are driven while being connected to an AC power source.

As described with reference to FIGS. 5 and 6, each of the light emitting cells comprises an N-type semiconductor layer, a P-type semiconductor layer and an active layer interposed therebetween. The semiconductor layers and the active layer may be formed as GaN based compound semiconductor layers. The semiconductor layers and the active layer are not limited to the GaN based compound semiconductor layer but may be formed of a variety of material films using various techniques.

The light emitting cells C₁ to C_(n) are connected in series, and nodes L₁ to L_(n-1) are positioned between light emitting cells. Switching blocks G₁ to G_(n-1) are connected to the nodes L₁ to L_(n-1), respectively. That is, the switching block G₁ is connected to the node L₁ between the light emitting cells C₁ and C₂, and the switching block G₂ is connected to the node L₂ between the light emitting cells C₂ and C₃. The switching block G_(n-1) is connected to the node L_(n-1) between the light emitting cells C₁ and C_(n) in such a manner.

As an AC voltage V_(ac) is increased in a forward direction, the switching blocks G₁ to G_(n-1) are sequentially operated to turn on the light emitting cells C₁ to C_(n) in sequence. Further, if the AC voltage passes a peak value and is decreased, the switching blocks G₁ to G_(n-1) are sequentially operated again to turn off the light emitting cells C₁ to C_(n) in sequence.

Each of the switching blocks G₁ to G_(n-1) is connected to source terminal S and ground terminal G of the array of the light emitting cells. Here, if an AC voltage power source is electrically connected to both ends of the array, a terminal through which a current flows into the array is referred to as the source terminal S and a terminal through which a current flows out from the array is referred to as the ground terminal G. The AC voltage power source may be connected to the source terminal S, and the ground terminal G may be grounded. Alternatively, the source and ground terminals S and G may be connected to both ends of the AC voltage power source, respectively. Here, for the sake of convenience of illustration, the ground terminal G will be described as being grounded. If the ground terminal G is grounded, the switching blocks G₁ to G_(n-1) may be separately grounded instead of being connected to the ground terminal G of the array.

The switching blocks G₁ to G_(n-1) can be driven by means of a voltage difference between the source and ground terminals S and G, and this operation will be described below.

When a voltage V_(ac) of the source terminal S is within a range of (Predetermined Voltage×n) to (Predetermined Voltage×(n+1)), each of the switching blocks G_(n) shorts the node L_(n) and the ground terminal G. Here, n denotes an ordinal number for a switching block. In this case, the switching blocks G₁ to G_(n-1) bypass a current to the ground terminal G. Meanwhile, if the voltage V_(ac) of the source terminal S is (Predetermined Voltage×(n+1)) or more, each of the switching blocks G_(n) opens the node L_(n) from the ground terminal G. In this case, the currents that are bypassed through the switching blocks G₁ to G_(n-1) are cut off. Further, if the voltage V_(ac) of the source terminal S is smaller than (Predetermined Voltage×n), each of the switching blocks G₁ to G_(n-1) opens the node L_(n) from the ground terminal G.

The predetermined voltage may be a forward voltage for the light emitting cells at a reference current. The reference current is determined in consideration of the light emitting efficiency of the light emitting cells. For example, the reference current may be determined as a current at which the light emitting efficiency of the light emitting cells is maximized. Such a current may be 15 to 25 mA and is 20 mA in GaN based semiconductor layers and active layers.

The operation of the light emitting device according to this embodiment will be described in detail below. Here, a forward voltage V_(f) for a light emitting cell at a reference current will be described as the predetermined voltage.

If an AC voltage power source is connected to the source terminal S so that a voltage of the source terminal becomes larger than the forward voltage V_(f), the switching block G₁ shorts the node L₁ and the ground terminal G. Accordingly, the reference current begins to flow through the light emitting cell C₁ and the switching block G₁, and the light emitting cell C₁ is operated to emit light. If the AC voltage V_(ac) further increases, a current exceeding the reference current flows through the light emitting cell C₁.

Subsequently, if the AC voltage reaches 2V_(f), the switching block G₁ opens the node L₁ from the ground terminal G to cut off a bypassing current. Meanwhile, the switching block G₂ shorts the node L₂ and the ground terminal G. Accordingly, the light emitting cell C₂ is turned on, and the reference current flows into the ground terminal G through the light emitting cells C₁ and C₂ and the switching block G₂. That is, the current is bypassed from the node L₂ to the ground terminal G by means of the switching block G₂.

As the AC voltage V_(ac) is increased, the processes in which the switching blocks G₁ to G_(n-1) are shorted and subsequently opened are repeated, so that the switching blocks G₁ to G_(n-1) are sequentially opened, and thus, the light emitting cells G₁ to G_(n) are sequentially turned on.

Meanwhile, if the AC voltage V_(ac) is decreased after a time of T/4 has been elapsed, the opened switching block G_(n-1) is shorted and the light emitting cell C_(n) is turned off. Subsequently, if the AC voltage V_(ac) is further decreased, the switching block G_(n-1) is opened, and the opened switching block G_(n-2) (not shown) is shorted to turn off the light emitting cell C_(n-1). That is, as the AC voltage V_(ac) is decreased, the processes in which the switching blocks G₁ to G_(n-1) are shorted and subsequently opened are repeated in sequence, and the light emitting cells are sequentially turned off.

Table 1 below summarizes the turn-on and turn-off operations of the light emitting cells with time for a ½ cycle.

Time C₁ C₂ C₃ . . . C_(n) Cn⁻¹ 0 off off off . . . off off on off off . . . off off on on off . . . off off on on on . . . off off on on on . . . on off T/4 on on on . . . on on on on on . . . on on on on on . . . on on on on on . . . on off on on on . . . off off on on off . . . off off on off off . . . off off T/2 Off off off . . . off off

Referring to Table 1, the light emitting cells C₁ to C_(n) are sequentially turned on with the lapse of time, and then turned off in reverse order after a time of T/4 has been elapsed. Under a driving voltage V_(ac) at which all light emitting cells are turned on in a prior art, all the light emitting cells according to this embodiment are also turned on. Additionally, according to this embodiment, some light emitting cells are turned on even before the driving voltage V_(ac) turns on all the light emitting cells.

Referring to FIG. 8, as the driving voltage V_(ac) is increased, the current flowing through the light emitting cells C₁ to C_(n) has a substantially constant current value until all the light emitting cells are turned on. The current substantially corresponds to the reference current. It will be apparent that if the driving voltage V_(ac) is further increased even after all the light emitting cells have been turned on, the current flowing through the light emitting cells are increased.

Meanwhile, since the light emitting cells are sequentially turned on, some of the light emitting cells emit light even when the driving voltage V_(ac) has a small value. Further, since the light emitting cells are sequentially turned off, some of the light emitting cells emit light even when the driving voltage V_(ac) has a small value. Thus, an effective time during which the light emitting cells are driven is increased.

According to this embodiment, as the light emitting cells C₁ to C_(n) are sequentially turned on and off, an effective time during which the light emitting cells are turned on to emit light is increased as a whole as compared with the prior art. Accordingly, if the same AC voltage power source as the prior art is used, light output is improved. In other words, even though a peak value of the driving voltage V_(ac) is set to be smaller as compared with the prior art, it is possible to provide the same light output as the prior art. Thus, the light emitting cells can be driven using a low current. Accordingly, the junction temperature of the light emitting cells can be lowered, thereby improving the light emitting efficiency.

The switching blocks G₁ to G_(n-1) are not limited to this embodiment but may be implemented into a variety of modifications. For example, the switching blocks may be configured as an identical circuit, and an additional circuit for sequentially operating the switching blocks may be added. Further, a circuit may be provided within or separately from the switching blocks to prevent an excessive current from flowing through operating light emitting cells when a source voltage V_(ac) increases in a certain voltage range. For example, such a circuit may include a constant voltage source such as a zener diode, or a resistor. Accordingly, it can be prevented that an excessive current flows through light emitting cells C₁ to C_(n-1) that have been turned on, before an arbitrary light emitting cell C_(n) is turned on.

Meanwhile, at least two arrays of light emitting cells connected in series may be connected in reverse parallel to each other and switching blocks may be connected to nodes between the light emitting cells of each of the arrays, respectively. Meanwhile, the switching blocks may be connected in common to the respective arrays. Accordingly, the switching blocks can allow the light emitting cells within one array to be sequentially turned on or off during a ½ cycle and then allow the light emitting cells within another array to be sequentially turned on and off during a latter ½ cycle.

FIG. 9 is a schematic circuit diagram illustrating an AC light-emitting device according to a second embodiment of the present invention, and FIG. 10 is a schematic graph illustrating a driving voltage and a light emission amount of the AC light-emitting device according to the second embodiment of the present invention.

Referring to FIG. 9, the AC light-emitting device according to this embodiment comprises an LED 200 and a switching block 300. The LED 200 comprises a plurality of arrays 101 to 108 each of which has light emitting cells connected in series. The arrays 101 to 108 are positioned on a single substrate, and each of the arrays has the different number of the light emitting cells connected in series and thus is driven at a different voltage level.

One terminal of each of the arrays 101 to 108 is connected to a first power source connection terminal 110, and the other terminals thereof are connected to a plurality of second power source connection terminals 121 to 128, respectively. Meanwhile, the switching block 300 is connected to the plurality of second power source connection terminals 121 to 128 of the light emitting diode 200 to form a current path between an external power source 1000 and one of the second power source connection terminals 121 to 128 in accordance with for example, voltage values of the external power source 1000. Here, the first power source connection terminal 110 is connected to the external power source 1000.

For example, the LED 200 comprises 8 light emitting cell arrays 101 to 108 as shown in FIG. 9, and a plurality of light emitting cells 30 are connected in series in each of the light emitting cell arrays 101 to 108 such that they emit light under a different voltage.

That is, each of the first to fourth arrays 101 and 104 has the different number of the light emitting cells 30 that are connected in series and connected in a forward direction between the second power source connection terminals 121 to 124 and the first power source connection terminal 110. Each of the fifth to eighth arrays 105 to 108 has the different number of the light emitting cells 30 that are connected in series and connected in a reverse direction between the second power source connection terminals 125 to 128 and the first power source connection terminal 110. At this time, the terms “forward direction” and “reverse direction” are intended to indicate the flow direction of a current between two terminals. A direction in which a current flows from the second power source connection terminals 121 to 128 to the first power source connection terminal 110 with respect to the second power source connection terminals 121 to 128 is referred to as the forward direction, and a direction in which a current flows from the first power source connection terminal 110 to the second power source connection terminals 121 to 128 is referred to as the reverse direction.

Here, the second array 102 has the light emitting cells 30 of which the number is larger than that of the first array 101, the third array 103 has the light emitting cells 30 of which the number is larger than that of the second array 102, and the fourth array 104 has the light emitting cells 30 of which the number is larger than that of the third array 103. Further, the sixth array 106 has the light emitting cells 30 of which the number is larger than that of the fifth array 105, the seventh array 107 has the light emitting cells 30 of which the number is larger than that of the sixth array 106, and the eighth array 108 has the light emitting cells 30 of which the number is larger than the seventh array 107. At this time, the first to fourth arrays 101, 102, 103 and 104 preferably comprise the light emitting cells 30 of which the numbers are identical with those of the fifth to eighth arrays 105, 106, 107 and 108, respectively.

For example, when a 220V AC power source 1000 is used, the number of the light emitting cells 30 within each of the first and fifth arrays 101 and 105 may be selected such that they emit light in a range where the absolute value of an AC voltage is 1 to 70V, the number of the light emitting cells 30 within each of the second and sixth arrays 102 and 106 may be selected such that they emit light in a range where the absolute value of an AC voltage is 71 to 140V, the number of the light emitting cells 30 within each of the third and seventh arrays 103 and 107 may be selected such that they emit light in a range where the absolute value of an AC voltage is 141 to 210V, and the number of the light emitting cells 30 within each of the fourth and eighth arrays 104 and 108 may be selected such that they emit light in a range where the absolute value of an AC voltage is 211 to 280V.

The aforementioned voltage range is only for illustrative purposes, and the voltage range can be adjusted by changing the number of the light emitting cells connected in series within light emitting cell arrays. The number of the light emitting cells determines a driving voltage of a light emitting cell array.

As shown in FIG. 9, the switching block 300 according to this embodiment comprises a first terminal connected to one end of the AC power source 1000 and a plurality of second terminals respectively connected to the plurality of second power source connection terminals 121 to 128. Further, the switching block 300 comprises a voltage level determination unit for determining a voltage level of the AC power source 1000, and a switch for changing a current path between the AC power source 1000 and the second power source connection terminals 121 to 128 depending on a voltage level. The switching block 300 is selectively bypassed to the second power source connection terminals 121 to 128 in accordance with a voltage applied in a forward or reverse direction.

The switching block 300 forms current paths between the second power source connection terminals 121 to 128 of the first to eighth arrays 101 to 108 and the AC power source 1000 depending on the voltage level of the AC power source 1000. For example, if a low forward voltage is applied, a current path is formed between the AC power source 1000 and the second power source connection terminal 121 of the first array 101 so that the light emitting cells within the first array 101 can emit light, and if a high reverse voltage is applied, a current path is formed between the AC power source 1000 and the second power source connection terminal 128 of the eighth array 108 so that the light emitting cells within the eighth array 108 can emit light.

FIG. 10 is a schematic graph illustrating a driving voltage and a light emission amount of the AC light-emitting device according to this embodiment. Here, FIG. 10 (a) shows waveforms diagram of an AC power source, and FIG. 10 (b) shows a light emission amount of the light emitting device.

Referring to FIG. 10, current paths between the AC current power source 1000 and the first to eighth arrays 101 to 108 are changed by the switching block 300 depending on a voltage level of the AC power source 1000. That is, any one of the first to eighth arrays 101 to 108 emits light at a certain level. Thus, since the light emitting device according to this embodiment emits light at most voltage levels of the AC power source 1000, an electric power loss and a flicker effect are reduced.

As shown in FIG. 10 (a), the voltage of the AC power source 1000 is periodically changed with time. When the AC power source is in a forward direction, a voltage level of the forward power source is defined as regions A, B, C and D, and an array capable of emitting light is determined depending on the regions. That is, if the voltage of the AC power source 1000 exists within the region A, a current path is formed to the first array 101 by the switching block 300 so that the light emitting cells within the first array 101 can emit light (See A′ in FIG. 10 (b)). Since a small number of the light emitting cells 30 are connected in series to each other in the first array 101, they are easily turned on with a small voltage. Further, if the voltage of the AC power source exists within the region B, a current path is formed to the second array 102 by the switching block 300 so that the light emitting cells within the second array 102 can emit light (See B′ in FIG. 10 (b)). Furthermore, if the voltage of the AC power source exists within the region C, a current path is formed to the third array 103 by the switching block 300 so that the light emitting cells within the third array 103 can emit light (See C′ in FIG. 10 (b)). In addition, if the voltage of the AC power source exists within the region D, a current path is formed to the fourth array 104 by the switching block 300 so that the light emitting cells within the fourth array 104 can emit light (See D′ in FIG. 10 (b)).

Meanwhile, when the AC power source is applied in a reverse direction, a voltage level of the reverse power source is defined as regions E, F, G and H, and an array capable of emitting light is changed depending on the regions. That is, current paths are selectively formed to the fifth to eighth arrays 105, 106, 107 and 108 by the switching block 300 in accordance with the voltage level of the AC power source 1000, so that the light emitting cells within each of the arrays can sequentially emit light (See E′, F′, G′ and H′ in FIG. 10 (b)).

FIG. 11 is a schematic circuit diagram illustrating an AC light-emitting device according to a third embodiment of the present invention, FIG. 12 is a schematic circuit diagram illustrating a modification of the AC light-emitting device according to the third embodiment of the present invention, and FIG. 13 is a schematic graph illustrating a driving voltage and a light emission amount of the AC light-emitting device according to the third embodiment of the present invention.

Referring to FIGS. 11 and 12, the AC light-emitting device according to this embodiment comprises a bridge rectifier 400 for rectifying a current from an AC power source 1000, a plurality of arrays 101 to 103 each of which has a plurality light emitting cells connected in series therein, and a switching block 300 connected to the arrays. The arrays 101 to 103 have the different numbers of light emitting cells.

Meanwhile, one terminal of each of the plurality of arrays 101 to 103 is connected to a first power source connection terminal 110 connected to the bridge rectifier 400, and the other terminals thereof are connected to a plurality of second power source connection terminals 121 to 123, respectively. The switching block 300 is connected to the plurality of second power source connection terminals 121 to 123 of the light emitting device 200 and the bridge rectifier 400. The switching block 300 forms current paths between the bridge rectifier 400 and the second power source connection terminals 121 to 123 depending on the level of a voltage to be rectified by the bridge rectifier 400.

As shown in FIG. 11, the bridge rectifier 400 may be formed with diode portions 410 to 440 disposed between the first to fourth nodes Q1 to Q4. That is, anode and cathode terminals of the first diode portion 410 are connected to the first and second nodes Q1 and Q2, respectively. Anode and cathode terminals of the second diode portion 420 are connected to the third and second nodes Q3 and Q2, respectively. Anode and cathode terminals of the third diode portion 430 are connected to the fourth and third nodes Q4 and Q3, respectively. Anode and cathode terminals of the fourth diode portion 440 are connected to the fourth and first nodes Q4 and Q1, respectively. The first and fourth diode portions 410 to 440 may have the same structure as the light emitting cells 30. That is, the first and fourth diode portions 410 to 440 may be formed on the same substrate while forming the light emitting cells 30. At this time, the first and third nodes Q1 and Q3 of the bridge rectifier 400 are connected to the AC power source 1000, the second node Q2 is connected to the switching block 300, and the fourth node Q4 is connected to the first power source connection terminal 110.

The bridge rectifier 400 may be provided using rectification diodes separate from the LED 200.

As shown in FIG. 12, the LED 200 may be positioned inside a bridge rectifier. This shows that a bridge rectifier 400 is manufactured using extra light emitting cells formed on edge portions of an LED chip upon manufacture of a light emitting diode comprising arrays each of which has a plurality of light emitting cells connected in series.

FIG. 13 is a schematic graph illustrating the operation of the AC light-emitting device according to the third embodiment of the present invention. Here, FIG. 13 (a) is waveforms diagram of the AC power source applied to the second node Q2 of the bridge rectifier 400, and FIG. 13 (b) is a graph illustrating a light emission amount of the light emitting device.

When an AC voltage is applied, a power source with a form in which a reverse voltage is reversed is produced through the rectification operation of the bridge rectifier 400, as shown in FIG. 13 (a). Accordingly, only a forward voltage is applied to the switching block 300. Thus, the arrays 101, 102 and 103 are connected in parallel to each other such that the LED 200 can emit light in response to the forward voltage.

If the level of a voltage of the AC power source rectified by the bridge rectifier 400 exists in a region A, a current path is formed to the first array 101 by the switching block 300 so that the light emitting cells within the first array can emit light. At this time, if the applied voltage is larger than the sum of threshold voltages of the light emitting cells 30 connected in series within the first array 101, light emission is started, and a light emission amount is increased as the applied voltage is increased. Thereafter, a current path is formed to the second array 102 by the switching block 300 if the voltage rises so that the voltage level reaches a region B, and a current path is formed to the third array 103 if the voltage level reaches a region C.

The AC light-emitting device according to this embodiment emits light at almost all the voltage levels of an AC power source without power consumption, and a time during which light is emitted is increased to reduce a flicker effect.

FIG. 14 is a circuit diagram illustrating an AC light-emitting device according to a fourth embodiment of the present invention. Hereinafter, n represents an integer of 2 or more.

Referring to FIG. 14, the light emitting device has an LED 200 and additionally, comprises first resistors R1 to Rn and second resistors R′1 to R′n.

The LED 200 comprises, on a single substrate, a plurality of first arrays A1 to An and a plurality of second arrays RA1 to RAn, each of which has the light emitting cells (30 in FIG. 5) connected in series. The first arrays A1 to An are connected in parallel to each other, and the second arrays RA1 to RAn are connected in reverse parallel to the first arrays.

The first arrays A1 to An have the different numbers of light emitting cells connected in series. That is, the number of the light emitting cells within the array A1 is smaller than that of the light emitting cells within the array A2, and the number of the light emitting cells within the array A2 is smaller than that of the light emitting cells within the array An. Further, the second arrays RA1 to RAn have the different numbers of light emitting cells connected in series. That is, the number of the light emitting cells within the array RA1 is smaller than that of the light emitting cells within the array RA2, and the number of the light emitting cells within the array RA2 is smaller than that of the light emitting cells within the array RAn.

The second arrays RA1 to RAn may have the light emitting cells of which the numbers correspond to those of the first arrays, respectively. That is, the array RA1 has the light emitting cells of which the number is identical with that of the array A1, the array RA2 has the light emitting cells of which the number is identical with that of the array A2, and the array RAn has the light emitting cells of the number is identical with that of the array An. Thus, the respective second arrays connected in reverse parallel are paired with the corresponding first arrays.

One end portions of the first and second arrays may be connected to one another on the substrate (20 in FIG. 5). To this end, a bonding pad (not shown) is provided on the substrate 20, and the end portions of the arrays may be connected to the bonding pad through wires. The wires for connecting the arrays to the bonding pad on the substrate 20 may be formed while forming the wires 41 in FIG. 5. Thus, it is unnecessary to connect the one end portions of the arrays through bonding wires, resulting in simplification of a wiring process.

Meanwhile, in the first and second arrays A1 to An and RA1 to Ran, an array having the greater number of the light emitting cells may have larger light emitting cells 30. That is, the light emitting cells within the same array may have the active layers (27 in FIG. 5) with substantially same sizes, but the light emitting cells within different arrays may have the active layers with different sizes. As the active layer 27 of the light emitting cell becomes large, the bulk resistance of the light emitting cell 30 is decreased. Accordingly, as a voltage is increased under a voltage larger than a threshold voltage, the amount of a current flowing through the light emitting cell 30 is rapidly increased.

Meanwhile, the first resistors R1 to Rn are connected in series to the first arrays A1 to An, respectively, and the second resistors R′1 to R′n are connected in series to the second arrays RA1 to RAn, respectively. The first and second resistors may be connected to the arrays through wires, respectively.

The first resistors R1 to Rn may have different resistance values, and the second resistors R′1 to R′n may also have different resistance values. At this time, it is preferred that the first and second resistors be respectively connected in series to the first and second arrays in such a manner that a resistor with a larger resistance value is connected to an array with the smaller number of the light emitting cells 30. That is, the resistor R1 or R′1 with a larger resistance value is connected in series to the array A1 or RA1 with the smaller number of the light emitting cells 30, and the resistor Rn or R′n with a smaller resistance value is connected in series to the array An or RAn with a greater number of the light emitting cells 30.

End portions of the resistors and end portions of the arrays are connected to both terminals of the AC power source 1000. Here, the AC power source 1000 may be a general household AC voltage power source. The operation of the AC light-emitting device will be described in detail below.

First, a half cycle in which a positive voltage is applied to the resistors and a negative voltage is applied to one end portion of each of the arrays opposite to the resistors by means of the AC power source will be described.

As an AC voltage is increased from a zero voltage, the first arrays A1 to An biased in a forward direction are turned on. Since the first arrays A1 to An have the different numbers of the light emitting cells 30, they are turned on, starting from the array A1 with the smaller number of the light emitting cells 30. The array A1 is turned on when the AC current exceeds the sum of threshold voltages of the light emitting cells within the array A1. As the AC voltage is increased, a current is increased to emit light. Meanwhile, if the AC voltage is further increased and thus the current is increased, a voltage drop due to the resistor R1 becomes larger. Accordingly, an excessive current is prevented from flowing through the array A1.

If the AC voltage is further increased and thus exceeds the sum of the threshold voltages of the light emitting cells within the array A2, the array A2 is turned on to emit light. As such a process is repeated, the array An is turned on to emit light. That is, the arrays are sequentially turned on, starting from an array with the smaller number of the light emitting cells 30.

Subsequently, if the AC voltage passes the maximum peak value at T/4 and then becomes smaller than the sum of the threshold voltages of the light emitting cells within the array An, the array An is turned off. Thereafter, the AC voltage is further decreased, so that the array A2 is turned off and the array A1 is then turned off. That is, the first arrays are sequentially turned off, starting from an array with the greater number of the light emitting cells 30. This is achieved in an order reverse to the order in which the arrays are turned on.

When the AC voltage becomes zero again, the half cycle is completed. In the latter half cycle, the second arrays RA1 to RAn that are biased in a forward direction as the phase of the AC voltage is changed are operated. The second arrays are operated in the same manner as the first arrays.

According to this embodiment, there is provided an AC light-emitting device driven by means of the AC power source 1000. Further, since the processes in which the first and second arrays A1 to An and RA1 to RAn are sequentially turned on and then turned off in the reverse order are repeated, a flicker effect can be reduced and a time during which the light emitting device emits light can be increased as compared with a conventional light emitting device.

Meanwhile, by connecting a resistor with a larger resistance value to an array with the smaller number of the light emitting cells, an excessive current can be prevented from flowing through an array that has been first turned on due to increase in the voltage.

Further, by connecting larger light emitting cells to an array with the greater number of the light emitting cells, it is possible to rapidly increase the amount of a current flowing through arrays that are turned on later according to increase in the voltage. That is, the bulk resistance of an array with the greater number of the light emitting cells may be smaller than that of an array with the smaller number of the light emitting cells. Thus, once an array with the greater number of the light emitting cells is turned on, a current flowing through the array is rapidly increased as the voltage is increased. Accordingly, an excessive current is prevented from flowing through an array that has been first turned on. Further, since an excessive current can be prevented by adjusting the sizes of light emitting cells, differences between the resistance values of the resistors can be reduced, and consequently, the resistance values of the resistors can be decreased. The decrease in the resistance values of the resistors causes increase in light output of the light emitting cells.

FIG. 15 is a schematic circuit diagram illustrating an AC light-emitting device according to a fifth embodiment of the present invention.

Referring to FIG. 15, the light emitting device has an LED 200 and additionally, has a common resistor Rt. The LED 200 has components that are substantially identical with those of the LED 200 described with reference to FIG. 14.

In the LED 200, one end portions of the first and second arrays A1 to An and RA1 to RAn may be connected to one another on the substrate 20 in FIG. 5, as described with reference to FIG. 14. Additionally, the other end portions of the first and second arrays may also be connected to one another on the substrate 20 in FIG. 5. The other end portions may be connected to a bonding pad (not shown) provided on the substrate 20 through wires, and the wires may be formed while forming the wires 41 of FIG. 5.

Meanwhile, instead of the first and second resistors R1 to Rn and R′1 to R′n in FIG. 14, the common resistor Rt is serially connected in common to the first and second arrays A1 to An and RA1 to RAn. At this time, the common resistor Rt may be connected on the bonding pad through a wire.

According to this embodiment, since the common resistor Rt is connected to the first and second arrays, a process of connecting a resistor is simplified as compared with the light emitting device of FIG. 14.

FIG. 16 is a schematic circuit diagram illustrating an AC light-emitting device according to a sixth embodiment of the present invention.

Referring to FIG. 16, the light emitting device has an LED 500 and a bridge rectifier 350, and may include resistors R1 to Rn.

The LED 500 comprises a plurality of arrays A1 to An each of which has light emitting cells 30 connected in series on the single substrate 20 in FIG. 5. The arrays A1 to An are connected in parallel to one another.

The arrays A1 to An have the different numbers of light emitting cells connected in series. That is, the number of the light emitting cells within the array A1 is smaller than that of the light emitting cells within the array A2, and the number of the light emitting cells within the array A2 is smaller than that of the light emitting cells within the array An.

One end portions of the arrays may be connected to one another on the substrate 20 in FIG. 5. To this end, a bonding pad (not shown) is provided on the substrate 20, and the end portions of the arrays may be connected to the bonding pad through wires. The wires for connecting the arrays to the bonding pad on the substrate 20 may be formed while forming the wires 41 in FIG. 5.

Further, in the arrays A1 to An, an array with the greater number of the light emitting cells may have larger light emitting cells 30.

The bridge rectifier 350 may be configured with light emitting cells identical with the light emitting cells 30. Thus, the light emitting cells of the bridge rectifier may be formed while forming the light emitting cells 30.

One end portions of the arrays A1 to An are connected in common to one node of the bridge rectifier 350. Such connection can be achieved by connecting the one node and the bonding pad through a wire.

Meanwhile, the resistors R1 to Rn may be connected in series to the arrays A1 to An, respectively.

The resistors R1 to Rn may have different resistance values. At this time, it is preferred that the resistors be respectively connected in series to the arrays in such a manner that a resistor with a larger resistance value is connected to an array with the smaller number of the light emitting cells 30. That is, the resistor R1 with a larger resistance value is connected in series to the array A1 with the smaller number of the light emitting cells 30, and the resistor Rn with a smaller resistance value is connected in series to the array An with the greater number of the light emitting cells 30.

As shown in this figure, one end portions of the resistors R1 to Rn are connected to another node of the bridge rectifier.

Both terminals of the AC power source 1000 are connected to two other nodes of the bridge rectifier 350, respectively. Here, the AC power source 1000 may be a general household AC voltage power source. The operation of the AC light-emitting device will be described below.

First, when a voltage is applied by the AC power source 1000, a positive voltage is applied to the resistors through the bridge rectifier 350 and a negative voltage is applied to one end portions of the arrays opposite to the resistors.

As an AC voltage is increased from a zero voltage, the first arrays A1 to An biased in a forward direction are turned on. Since the first arrays A1 to An have the different numbers of the light emitting cells 30, they are turned on, starting from the array A1 with the smaller number of the light emitting cells 30. The array A1 is turned on when the AC current exceeds the sum of threshold voltages of the light emitting cells within the array A1. As the AC voltage is increased, a current is increased to emit light. Meanwhile, if the AC voltage is further increased and thus the current is increased, a voltage drop due to the resistor R1 becomes larger. Accordingly, an excessive current is prevented from flowing through the array A1.

If the AC voltage is further increased and thus exceeds the sum of the threshold voltages of the light emitting cells within the array A2, the array A2 is turned on to emit light. As such a process is repeated, the array An is turned on to emit light. That is, the arrays are sequentially turned on, starting from an array with the smaller number of the light emitting cells 30.

Subsequently, if the AC voltage passes the maximum peak value at T/4 and then becomes smaller than the sum of the threshold voltages of the light emitting cells within the array An, the array An is turned off. Thereafter, the AC voltage is further decreased, so that the array A2 is turned off and the array A1 is then turned off. That is, the first arrays are sequentially turned off, starting from an array with the greater number of the light emitting cells 30. This is achieved in an order reverse to the order in which the arrays are turned on.

When the AC voltage becomes zero again, the half cycle is completed. Even in the latter half cycle, the arrays A1 to An are operated in the same manner by the bridge rectifier 350.

According to this embodiment, there is provided an AC light-emitting device driven by means of the AC power source 1000. Further, since the processes in which the arrays A1 to An are sequentially turned on and then turned off in the reverse order are repeated, a flicker effect can be reduced and a time during which the light emitting device emits light can be increased as compared with a conventional light emitting device.

Although the resistors R1 to Rn are respectively connected in series to the arrays A1 to An in this embodiment, the common resistor Rt instead of the resistors R1 to Rn may be connected as shown in FIG. 15. In this case, the end portions of the arrays A1 to An may be connected to one another on the substrate 20 in FIG. 5.

Meanwhile, in the aforementioned embodiments, the number of the light emitting cells or a difference in size between the light emitting cells generates a difference in relative luminous intensity between the arrays. That is, since an array that is first turned on has the smaller number of the light emitting cells, overall luminous intensity thereof is relatively weak. Moreover, since an array that is finally turned on has the greater number of the light emitting cells, luminous intensity thereof is relatively strong. Such a difference may be enlarged due to differences in the sizes of the light emitting cells and the resistors. Although there is an advantage in that the arrays are early turned on, the luminous intensity of the arrays initially turned on is relatively small. Thus, it may not greatly contribute to reduction in the flicker effect. Thus, it is necessary to increase the luminous intensity of the arrays initially turned on. To this end, the structures of the light emitting cells within the respective arrays may be constructed differently. FIGS. 17 and 18 are sectional views illustrating LEDs in which the structures of light emitting cells within some arrays are modified to increase the luminous intensity of the light emitting cells within the arrays.

Referring FIG. 17, the LED according to this embodiment is substantially identical with that described with reference to FIG. 5, and the light emitting cell arrays may be arranged in the same manner as the first to sixth embodiments. However, the light emitting cell in this embodiment is different from that of FIG. 5 in that a top surface of the light emitting cell, e.g., the surface of a second conductive type semiconductor layer 29 a, is roughened.

Light emitting cells each of which has the second conductive type semiconductor layer 29 a with the roughened surface may construct the arrays in the first and sixth embodiments of the present invention, which have been previously described above. Further, in the first and sixth embodiments, arrays of which the number is ½ or less of the number of entire arrays may be constructed of the light emitting cells having the second conductive type semiconductor layers 29 a with the roughened surfaces. For example, arrays of which the number is ½ or less of the number of the first arrays and arrays of which the number is ½ or less of the number of the second arrays in FIGS. 14 and 15 may be constructed of the light emitting cells having the second conductive type semiconductor layers 29 a with the roughened surfaces; and arrays of which the number is ½ or less of the number of the arrays in FIG. 16 may be constructed of the light emitting cells having the second conductive type semiconductor layers 29 a with the roughened surfaces. At this time, the light emitting cells having the second conductive type semiconductor layers 29 a with the roughened surfaces constitute arrays having the smaller number of the light emitting cells, and arrays having the greater number of the light emitting cells are constructed of light emitting cells having flat surfaces.

The second conductive type semiconductor layer 29 a with the roughened surface may be formed by sequentially forming a first conductive type semiconductor layer 25, an active layer 27 and the second conductive type semiconductor layer, and etching a region of the second conductive type semiconductor layer using a photoelectrochemical etching technique. Meanwhile, the roughened surface may be formed by forming a metallic thin film, e.g., with a thickness of 10 to 500 Å, in a region of the second conductive type semiconductor layer and performing heat treatment and etching of the metallic thin film.

Thereafter, the array(s) of the light emitting cells each of which has the second conductive type semiconductor layer 29 a with the roughened surface is formed by etching the region of the semiconductor layers to form the light emitting cells and electrically connecting the light emitting cells to one another.

Meanwhile, an electrode pad 33 b is formed on the second conductive type semiconductor layer 29 a with the roughened surface, and the electrode 31 in FIG. 5 may also be formed thereon.

The arrays each of which has the smaller number of the light emitting cells, e.g., the arrays A1 and RA1 of FIGS. 14 and 15 or the array A1 of FIG. 16, are constructed of the light emitting cells having the roughened surfaces, so that the luminous intensity of these arrays can be increased. Thus, since the luminous intensity of the arrays A1 and RA1 that are initially turned on when an AC voltage is applied thereto is large, a flicker effect can be further reduced.

The roughened surface may be formed on a bottom surface of the substrate of FIG. 6. Alternatively, the substrate 20 may be separated in FIG. 6 and the roughened surface may be formed on a bottom surface of the first conductive type semiconductor layer 25.

Referring to FIG. 18, light emitting cells in this embodiment are substantially identical with those described with reference to FIG. 5, and light emitting cell arrays may be arranged in the same manner as described in the first to sixth embodiments. However, in this embodiment, each of the light emitting cells is formed to have inclined side surfaces. The light emitting cells each of which has the inclined side surfaces constitute the arrays (A1 and RA1 in FIGS. 14 to 17) that are initially turned on in the same manner as the light emitting cells having the roughened surfaces, and may constitute arrays of which the number is ½ of the number of the first and second arrays in FIGS. 14 to 17.

The inclined side surfaces may be formed by reflowing a photoresist pattern, and then etching the semiconductor layers using the photoresist pattern as an etching mask, in the separation process of the light emitting cells after the formation of semiconductor layers. Additionally, the inclined side surfaces may be formed by performing reflow of the photoresist pattern and etching the second conductive type semiconductor layer and the active layer when a region of the first conductive type semiconductor layer 25 is exposed.

The inclined side surfaces of the light emitting cells can reduce a light loss due to total reflection, thereby improving luminous intensity of the light emitting cells. Thus, by forming arrays, which are initially turned on, out of such light emitting cells, a flicker effect can be reduced as described with reference to FIG. 17.

FIG. 19 is a sectional view illustrating an AC light-emitting device 1 according to a seventh embodiment of the present invention.

Referring to FIG. 19, the light emitting device 1 comprises an LED chip 3. The LED chip 3 has a plurality of light emitting cells connected in series. Each of the light emitting cells may be an Al_(x)In_(y)Ga_(z)N based compound semiconductor capable of emitting ultraviolet or blue light. The structures of the LED chip 3 and the light emitting cells are identical with those described with reference to FIG. 5 or 6. The light emitting cells are connected in series and constitute an array. The LED chip 3 may comprise two arrays connected in reverse parallel, or may comprise a bridge rectifier, so that it can be driven by means of an AC power source.

The LED chip 3 is electrically connected to an external power source through lead terminals (not shown). To this end, the LED chip 3 may have two bonding pads (not shown) used for connection to the lead terminals. The bonding pads are connected to the lead terminals through bonding wires (not shown). On the contrary, the LED chip 3 may be flip-bonded to a submount substrate (not shown) and then electrically connected to the lead terminals through the submount substrate.

Meanwhile, the LED chip 3 may be positioned within a reflection cup 9. The reflection cup 9 reflects light emitted from the LED chip 3 in a range of desired viewing angles to increase luminance within a certain range of viewing angles. Thus, the reflection cup 9 has a predetermined inclined surface depending on a required viewing angle.

Meanwhile, phosphors 7 are positioned over the LED chip 3 and then excited by light emitted from the light emitting cells to emit light in a visible light range. The phosphors 7 include a delay phosphor. The delay phosphor may have a decay time of 1 msec or more, preferably, about 8 msec or more. Meanwhile, an upper limit of the decay time of the delay phosphor can be selected depending on uses of light emitting devices and may be, but not specifically limited to, 10 hours or less. Particularly, in case of a light emitting device used for general household illumination, the decay time of the delay phosphor is preferably a few minutes or less.

The delay phosphor may be a silicate, an aluminate, a sulfide phosphor or the like disclosed in U.S. Pat. Nos. 5,770,111, 5,839,718, 5,885,483, 6,093,346, 6,267,911 and the like. For example, the delay phosphor may be (Zn,Cd)S:Cu, SrAl₂O₄:Eu,Dy, (Ca,Sr)S:Bi, ZnSiO₄:Eu, (Sr,Zn,Eu,Pb,Dy)O.(Al,Bi)₂O₃, m(Sr,Ba)O_(n)(Mg,M)O₂(Si,Ge)O₂:Eu,Ln (wherein, 1.5≦m≦3.5; 0.5≦n≦1.5; M is at least one element selected from the group consisting of Be, Zn and Cd; and Ln is at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Th, Dy, Ho, Er, Tm, Yb, Lu, B, Al, Ga, In, Tl, Sb, Bi, As, P, Sn, Pb, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Cr and Mn), or the like.

The delay phosphor is excited by light emitted from the LED chip 3 to emit light in the visible light range, e.g., red, green and/or blue light. Accordingly, it is possible to provide a light emitting device capable of emitting light having various colors by mixing light emitted from the LED chip 3 with light emitted from the delay phosphor, and to provide a light emitting device capable of emitting white light.

Meanwhile, the phosphors 7 may include other phosphors capable of emitting light in the visible light range while being excited by light from the LED chip 3, e.g., red, green and/or blue phosphors, or yellow phosphors, in addition to the delay phosphor. For example, the other phosphors may be YAG:Ce based phosphors, orthosilicate based phosphors, or sulfide phosphors.

The delay phosphors and the other phosphors are selected such that the light emitting device emits light having a desired color. In case of a white light emitting device, the delay phosphor and the other phosphors may be formed of various combinations of phosphors such that light obtained by mixture of light emitted from the LED chip 3 with converted light becomes white light. Further, a combination of the delay phosphor and the other phosphors may be selected in consideration of flicker effect prevention, light emitting efficiency, a color rendering index, and the like.

Meanwhile, a transparent member 5 may cover the LED chip 3. The transparent member 5 may be a coating layer or a molded member formed using a mold. The transparent member 5 covers the LED chip 3 to protect the LED chip 3 from external environment such as moisture or an external force. For example, the transparent member 5 may be made of epoxy or silicone resin. In a case where the LED chip 3 is positioned within the reflection cup 9, the transparent member 5 may be positioned within the reflection cup 9 as shown in this figure.

The phosphors 7 may be positioned between the transparent member 5 and the LED chip 3. In this case, the transparent member 5 is formed after the phosphors 7 have been applied to the LED chip 3. On the contrary, the phosphors 7 may be dispersed within the transparent member 5 as shown in this figure. There have been known a variety of techniques of dispersing the phosphors 7 within the transparent member 5. For example, the transparent member 5 may be formed by performing transfer molding using mixed powder with phosphors and resin powder mixed therein, or by dispersing phosphors within liquid resin and curing the liquid resin.

FIG. 20 is a schematic graph illustrating a light emitting characteristic of an AC light-emitting device according to an embodiment of the present invention. Here, a dotted line (a) is a curve schematically illustrating a light emitting characteristic of a conventional AC light-emitting device, and a solid line (b) is a curve schematically illustrating a light emitting characteristic of a light emitting device according to the embodiment of the present invention.

Referring to FIG. 20, the conventional light emitting device that does not employ a delay phosphor periodically repeats on-off by means of application of an AC voltage thereto. Assuming that the period of an AC power source is T, two arrays each of which has light emitting cells connected in series are alternately operated once during the period T. Thus, the light emitting device emits light with a period of T/2 as represented by the dotted line (a). Meanwhile, if the AC voltage does not exceed a threshold voltage of the light emitting cells connected in series, the light emitting cells are not operated. Thus, the light emitting cells remain in a turned-off state for a certain time, i.e., for a time during which the AC voltage is smaller than the threshold voltage thereof, between times during which the light emitting cells are operated. Accordingly, a flicker effect may appear in the conventional light emitting device due to gaps between times during which the light emitting cells are operated.

On the other hand, since the light emitting device according to the embodiment of the present invention employs a delay phosphor, light is emitted even while the light emitting cells remain in the turned-off state as represented by the solid line (b). Thus, although there is a change in luminous intensity, a time during which light is not emitted becomes shorter, and the light emitting device continuously emits light if the decay time of the delay phosphor is long.

When a general household AC power source applies a voltage with a frequency of about 60 Hz, one cycle of the power source is about 16.7 msec and a half cycle is 8 msec. Thus, while the light emitting device is in operation, a time during which all the light emitting cells are turned off is smaller than 8 msec. Accordingly, if the decay time of the delay phosphor is 1 msec or more, a flicker effect can be sufficiently reduced. Particularly, if the decay time of the delay phosphor is similar to a time during which all the light emitting cells are turned off, the light emitting device can continuously emit light.

FIG. 21 is a diagram of an illumination system according to an exemplary embodiment of the present invention.

An illumination system 2000 may include a controller 2100 and a light emitting unit 2200. The light emitting unit 2200 may include a first light emitting device 2210, a second light emitting device 2220, . . . , and a nth light emitting device 2230.

The light emitting device 2210, the second light emitting device 2220, . . . , and the nth light emitting device 2230 are arranged in an area (for example, area 2500 as described below with respect to FIGS. 23-28) spaced apart from each other. An operational status of each light emitting device may be controlled by the controller 2100 to illuminate the area 2500.

By independently controlling the operational status of the first light emitting device 2210, the second light emitting device 2220, . . . , and the nth light emitting device 2230 with the controller 2100, illumination of the area 2500 may be varied.

Each of the first light emitting device 2210, the second light emitting device 2220, . . . , and the nth light emitting device 2230 may include a light emitting module 2212, a driving unit 2214, and a sensing information processing unit 2216.

The light emitting module 2212 may be driven by AC power. The light emitting module 2212 may include a light emitting diode array including multiple light emitting diodes connected in series.

The light emitting module 2212 may include: a plurality of light emitting diode arrays, similar to arrays 101, 102, 103 and 104, described above with reference to FIG. 9, each array including a plurality of light emitting diodes connected in series in a forward direction; and a plurality of light emitting diode arrays, similar to arrays 105, 106, 107 and 108 described above with reference to FIG. 9, each array including a plurality of light emitting diodes connected in series in a backward direction. Thus, the arrays connected in the forward direction may be connected in anti-parallel to the arrays connected in the backward direction. The light emitting module 2212 may further include a switching unit, similar to switching unit 300 described above with reference to FIG. 9, connected between an AC power source, similar to AC power source 1000, described above with reference to FIG. 9, to control operation of the light emitting diode arrays based on a voltage state of the AC power source.

As described above with reference to FIG. 14, instead of providing a switching unit, resistors, similar to resistors R₁ to R_(n) and R′₁ to R′_(n), may be connected to the light emitting diode arrays. Thus, it may be possible to control the light emitting diode arrays of the light emitting module 2212 based on a voltage state of the AC power source, similar to AC power source 1000.

The driving unit 2214 may include a rectifying unit, similar to rectifying unit 400, described above with reference to FIG. 11, for rectifying the AC power source. Thus, the light emitting module 2212 may include light emitting diode arrays, similar to arrays 101 to 103 described above with reference to FIG. 11, including light emitting diodes connected in one direction. Further, a switching unit, similar to switching unit 300 described above with reference to FIG. 11, may be connected between the rectifying unit and the light emitting diode arrays in order to control operations of the light emitting diode arrays based on a voltage state of the AC power source.

As described above with reference to FIG. 16, instead of providing a switching unit, resistors similar to resistors R₁ to Rn, may be connected to the light emitting diode arrays. Thus, it may be possible to control the light emitting diode arrays of light emitting module 2212 based on a voltage state of the AC power source.

The driving unit 2214 supplies various driving voltages to the light emitting module 2212. The driving unit 2214 may supply a driving control signal controlled by a user or the controller 2100, thereby controlling an operational status of the light emitting module 2212. The driving unit 2214 may control the operational status of the light emitting module 2212 based on a dimming control signal or a turn-on/turn-off control signal inputted by the user through a switching controller (not shown) or the like. The driving unit 2214 may control the operational status of the light emitting module 2212 based on a driving control signal generated by the controller 2100.

The driving unit 2214 may control the operational status of the light emitting module 2212 based on sensing information received from a sensing information processing unit 2216.

The sensing information processing unit 2216 collects various sensing information sensed by various types of sensors (not shown) in the area 2500. The sensing information processing unit 2216 sends the collected sensing information to the controller 2100. The sensors may be included in the light emitting device 2210. The various sensing information within the area 2500 may be collected by using a light sensor to detect brightness of the area, a motion sensor to detect a motion of an object moving in the area 2500, and the like. The moving object may include a car, a person, an animal, etc.

The sensing information processing unit 2216 may receive brightness information from light sensors distributed in the area 2500. Information about a moving direction of the object or information about a speed of the object may be received from motion sensors distributed in the area 2500. The motion sensor may calculate the speed of the object based on a reflection wave of an electromagnetic wave irradiated to the object. The motion sensor may also detect position information of the object by analyzing information from the reflection wave of the electromagnetic wave irradiated to the object or analyzing image information of the object.

The controller 2100 may control the operational status of each light emitting device based on the various sensing information received from the sensing information processing unit 2216 of each light emitting device 2210, 2220, . . . , and 2230. The controller 2100 may establish at least one group including one or more light emitting devices and may control the operational status of the groups independently.

FIG. 22 is a diagram of a controller according to an exemplary embodiment of the present invention.

The controller 2100 may include a reception unit 2110, an information management unit 2120, a data storage unit 2130, a control signal generation unit 2140, and an output unit 2150.

The reception unit 2110 receives the various sensing information from the sensing information processing unit 2216 of each light emitting device 2210, 2220, . . . , and 2230 and sends the received information to the information management unit 2120. The reception unit 2110 may receive brightness information from the light sensor or motion information of the object from the motion sensor. Time information indicating a time when each sensing information is received may also be received by the reception unit 2110. The reception unit 2110 may receive sensing information directly from sensors installed in the area 2500 or in the light emitting devices 2210, 2220, . . . , and 2230.

The information management unit 2120 stores in the data storage unit 2130 the various sensing information for the area 2500 that are received from the reception unit 2110. Brightness information received from the light sensor may be stored in the form of a matching table which matches the brightness information with position information or identification information of the light sensor. Identification information of the light emitting devices 2210, 2220, . . . , and 2230 may be also be stored in the matching table.

Speed information of the object detected by the motion sensor, or position information of the object and time information indicating a time when the position information is detected may be stored in the data storage unit 2130.

The data storage unit 2130 may store therein position information of the area 2500 in which the light emitting devices 2210, 2220, . . . , and 2230 are located and position information of the area 2500 in which the sensors are located. Further, the information recorded by the information management unit 2120, such as the brightness information of the area 2500, the speed information of the object, the position information of the object, or the time information indicating the time when each information is collected, may be stored in the data storage unit 2130.

The control signal generation unit 2140 generates a control signal to control the driving of the light emitting unit 2200 based on the various information stored in the data storage unit 2130 or the like.

The control signal generation unit 2140 may generate a control signal to control an illumination state of the light emitting device matched to each area 2500 based on the brightness information of each area 2500. Based on the illumination state of each area 2500, light emitting devices whose operational statuses may be controlled identically may be grouped together. Once grouped together the operational statuses of the light emitting devices belonging to the same group may be identically controlled. Thus, control efficiency of the controller 2100 may be improved. Moreover, since it is possible to adjust an illumination state of each group based on an external condition, such as, brightness, energy consumption efficiency may also be improved.

The output unit 2150 sends the control signal generated by the control signal generation unit 2140 to the light emitting unit 2200.

FIG. 23 is a diagram of an illumination adjustment method according to an exemplary embodiment of the present invention.

A plurality of light emitting devices 2210 and a plurality of light sensors 2310 may be installed in an area 2500. Although the light emitting sensors 2310 are depicted as separated from the light emitting devices 2210, the light sensors 2310 may be combined with the light emitting devices 2210. Further, each light emitting device 2210 in the area 2500 may be incorporated into a light emitting unit 2200 as described above with respect to FIG. 21 and FIG. 22.

Illumination states at different positions in the area 2500 may differ, for example, depending on a distance from a light source such as the sun. A first position close to sun light may be brighter than a second position further from sun light. In view of this difference, in order to adjust illumination states, the area 2500 may be divided into groups, in which multiple groups of light emitting devices 2210 may be respectively arranged based on brightness information sensed by light sensors 2310 or the like. Thus, a first group 2510 may include light emitting devices 2210 located in the first position close to the sunlight; a second group 2520 may include light emitting devices 2210 located in the second position farther from the sun light than the light emitting devices 2210 of the first group 2510; and a third group 2530 may include light emitting devices 2210 located in a third position farthest from the sun light. The number of the light emitting devices 2210 in each group may vary.

Illumination of the light emitting devices 2210 in the respective groups may be controlled as follows. The brightness of the light emitting devices 2210 in the first group 2510 may be set to be relatively lower than that of the light emitting devices 2210 in the second group 2520 and the third group 2530, the brightness of the light emitting devices 2210 in the second group 2520 may be set to be relatively higher than that of the light emitting devices 2210 in the first group 2510, and the brightness of the light emitting devices 2210 in the third group 2530 located farthest from sun light may be set to be relatively higher than the brightness of the second group 2520. By adjusting illumination states of the light emitting devices 2210 depending on the degree of brightness in the area 2500, power consumption may be reduced.

The illumination state of each light emitting device 2210 can be adjusted by controlling the driving of light emitting diode arrays included in each light emitting module 2212.

FIG. 24 is a diagram of a light emitting module according to an exemplary embodiment of the present invention. FIG. 24 depicts a light emitting module and light emitting devices of the illumination adjustment method of FIG. 23. FIG. 24 may depict the light emitting module described with respect to FIG. 21.

As shown in FIG. 24( a), the light emitting module 2212 included in each light emitting device 2210 has a plurality of light emitting diode arrays each having a different number of light emitting diodes. A specific light emitting diode array to be operated may be selected by applying a switching signal S1, S2, S3, . . . , Sn, thus controlling the brightness of the light emitting module 2210.

FIG. 24( b) illustrates a first light emitting device 2210 of the first group 2510, a second light emitting device 2220 of the second group 2510, and a third light emitting device 2230 of the third group 2230. Depending on the brightness of the external light source, the brightness of each light emitting device 2210, 2220, and 2230 may be adjusted by controlling the operation of the light emitting diode arrays of each light emitting device 2210, 2220, and 2230. With respect to FIG. 23, when the external light source is brighter than a reference value the brightness of the light emitting devices in the first group 2510 located closest to the external light may be dimmed, whereas the brightness of the light emitting devices 2220 and 2230 in the second group 2520 and third group 2530 located further from the external light may be brightened. In such a case, in each light emitting device 2210 of the first group 2510, a light emitting diode array including two light emitting diodes may be operated; in each light emitting device 2220 of the second group 2520, a light emitting diode array including three light emitting diodes may be operated; and in each light emitting device 2230 of the third group 2530, a light emitting diode array including four light emitting diodes may be operated. Thus, the brightness of the light emitting devices 2210, 2220, and 2230 may be increased. The operational statuses of the light emitting diode arrays of the light emitting devices 2210, 2220, and 2230 may be controlled based on each group such that the number of the light emitting diodes in operation increases as the distance from the external light source increases.

The controller 2100 may increase the number of groups if the brightness of the external light source decreases, and the controller 2100 may independently set the brightness of the one or more light emitting devices belonging to each group.

A control signal for adjusting illumination may be generated based on motion information of an object.

FIG. 25 is a diagram of an illumination adjustment method according to an exemplary embodiment of the present invention.

As shown in FIG. 25, an area 2500 is a space having an entrance and an exit and elongated in a lengthwise direction with a reference width and a reference length. For example, the area 2500 may be a tunnel through which a car passes. Since a part of the area 2500 may be isolated from the external light source, the amount of external light that reaches respective light emitting devices may vary.

A motion sensor (not shown) for detecting a motion of an object as well as a light sensor for detecting brightness may be provided in area 2500 to provide sensing information.

The motion sensor may collect position information, speed information or moving direction information of an object 2550 as the object 2550 moves through the area 2500. The controller 2100 described above with respect to FIG. 22 may utilize the sensing information in conjunction with the illumination system described above with respect to FIG. 21.

The control signal generation unit 2140 may calculate the moving direction information or the speed information of the object 2550 based on the position information of the object 2550 and time information indicating a time when the position information of the object 2550 is collected. The position information and the time information may be read from the data storage unit 2130.

The controller 2100 divides the light emitting devices arranged in the area 2500 into one or more groups and adjusts illumination states thereof by groups. The number of light emitting devices belonging to each group may be varied depending on a setting of the controller 2100, for example, to ensure substantially the same illumination effect over the entire area 2500, by varying the illumination in each group. Although the numbers of the light emitting devices included in the respective groups may vary, the total number of the light emitting devices installed in the area 2500 is fixed. Thus, by adjusting the number of light emitting devices included in each group, the area covered by each group may be changed.

If the number of the light emitting devices included in one group increases, the area covered by that group may be enlarged. On the other hand, if the number of the light emitting devices decreases, the area covered by that group may be reduced.

Depending on brightness information of the area 2500, the controller 2100 may establish a first group 2510 including light emitting devices positioned adjacent to the entrance of the area 2500, a second group 2530 including light emitting devices positioned adjacent to the exit of the area 2500, and an third group 2520 including light emitting devices positioned between the first group 2510 and the second group 2530. This configuration may be established based on a reference value at a reference operational stage of the illumination system 2000 regardless of the brightness outside the area.

The number of the light emitting devices included in the first group 2510, the second group 2530, and the third group 2520 may be varied depending on the brightness outside the area 2500. If each light emitting device within the area 2500 does not illuminate or illuminates according to a reference brightness level, actual brightness at the respective positions in the area 2500 may differ.

The brightness at a position adjacent to the entrance or the exit of the area 2500 may be higher than the brightness at an inner position of the area 2500. Accordingly, it may be desirable to control the brightness at the position adjacent to the entrance or the exit of the area 2500 to be lower than that at an inner position.

The controller 2100 may divide the light emitting devices into groups based on the outside brightness information, inside brightness information of the area 2500, and the like. The controller 2100 may adjust the illumination state of the each group to be different from the illumination states of other groups.

The controller 2100 may adjust the number of light emitting devices belonging to the first group 2510 or the second group 2530 depending on the outside brightness, thereby adjusting the number of light emitting devices belonging to the third group 2520. If the brightness of the outside is lower than a first reference value, the number of the light emitting devices belonging to the first group 2510 or the second group 2530 may be reduced to below a first initial value. On the other hand, if the outside brightness is equal to or higher than the first reference value, the number of the light emitting devices belonging to the first group 2510 or second group 2530 may be increased to be equal to or larger than the first initial value.

The brightness of the light emitting devices included in the third group 2520 may be set to be higher than the brightness of the light emitting devices included in the first group 2510 or second group 2530. Further, the third group 2520 may be divided into one or more groups. If there is a great variation in the brightness within the area, which may occur depending on the distance from the entrance or the exit, the third group 2520 may be divided into multiple intermediate groups and brightness of the light emitting devices may be controlled for each of the multiple intermediate groups. The controller 2100 may adjust the number of the intermediate groups depending on the brightness inside of the area. As the discrepancy in the brightness between positions inside the third group 2520 increases, the number of the intermediate groups may be increased.

It may be possible to adjust the brightness of the light emitting devices in each group. The brightness of the light emitting devices in the first group 2510 or in the second group 2530 may be adjusted depending on the outside brightness. If the outside brightness is lower than a second reference value, the brightness of the light emitting devices of the first group 2510 or the second group 2530 may be increased to be equal to or larger than a second initial value, whereas if the outside brightness is equal to or higher than the second reference value, the brightness of the light emitting devices of the first group 2510 or the second group 2530 may be reduced to be below the second initial value.

The controller 2100 may adjust the number of the light emitting devices belonging to each group based on a speed of an object (e.g., a car) 2550 as well as the outside brightness.

FIG. 26 is a diagram of an illumination adjustment method according to an exemplary embodiment of the present invention.

In FIG. 26( a) and FIG. 26( b), the controller 2100 (as described above with respect to FIG. 22) varies an illumination area of each group by varying the number of light emitting devices belonging to each group based on the speed of the object 2550. The area 2500 may be a tunnel and the object 2250 may be a car traveling through the tunnel.

In FIG. 26( a), the controller 2100 establishes a first group 2512, a second group 2532, and multiple intermediate groups 2521, 2522 and 2523 to have the same number of light emitting devices for illuminating an area of same size. The brightness of the first group 2512 and the second group 2532 may be the lowest, and the brightness of the intermediate group 2522, farthest from the entrance and the exit, may be the highest.

If the speed of the car 2550 travelling in the tunnel 2500 increases, the number the light emitting devices of the first group 2512 and the number of the light emitting devices of the second group 2532 may be decreased, while the number of the light emitting devices of the intermediate groups may be increased. Thus, a brighter illumination state may be provided throughout the area 2500 for the safety of a driver.

In contrast, if the speed of the car 2250 in the tunnel 2500 decreases due to a traffic jam or the like, the illumination states of the groups may be adjusted in the opposite manner.

If a speed of the car 2550 that enters through the entrance of the tunnel 2500 is equal to or greater than a third reference value, the number of the light emitting devices belonging to the first group 2510 or the second group 2530 may be reduced to below a third initial value. On the other hand, if the speed of the car 2550 is below the third reference value, the number of the light emitting devices belonging to the first group 2510 or the second group 2530 may be increased to be equal to or larger than the third initial value.

FIG. 27 is diagrams of an illumination adjustment method according to an exemplary embodiment of the present invention.

The illumination adjustment method of FIG. 27 is designed for application to various types of illumination equipment provided in an environment in which a speed of an object 2560 may be relatively low. Such illumination equipment may be, but is not limited to, street lamps or indoor lighting. In FIG. 27, an area is a space elongated in a lengthwise direction with a reference length and a reference width.

The controller 2100 (as described above with respect to FIG. 22) adjusts an illumination state of each light emitting device based on brightness information detected by a sensor. When the outside brightness is high, the light emitting devices may not be operated or a light emitting diode array including the smallest number of light emitting diodes may be driven. When the outside brightness is low, on the other hand, a light emitting diode array including the larger number of light emitting diodes may be operated, thus adjusting brightness of the area.

If no motion of the object 2560 is detected in the area in the low outside brightness state, a reference brightness level may be maintained. If the object 2560 approaches the area 2500, brightness of the light emitting devices may be gradually increased.

FIG. 28 is a diagram of a light emitting module according to an exemplary embodiment of the present invention.

FIG. 28 depicts the number of light emitting diode arrays operated in the light emitting module of light emitting device 2210 as an object approaches and enters the area 2500. In FIG. 28, the controller 2100 drives a light emitting diode array including a number of light emitting diodes as the object 2560 approaches the light emitting device 2210 (as described above with reference to FIG. 22). If no object is detected near light emitting device 2210, a reference brightness level may be maintained by operating a light emitting diode array including only two light emitting diodes. If it is detected that the object 2560 is approaching the light emitting device 2210, a light emitting diode array including three light emitting diodes may be driven, thus increasing brightness of the light emitting device 2210. As the object 2560 gets closer to the light emitting device 2210, a light emitting diode array including four light emitting diodes may be operated, thus further increasing the brightness of the light emitting device 2210.

It may be possible to use a driving method to gradually increase the brightness of the light emitting device 2210 as the object 2560 approaches the light emitting device 2210. In contrast, if the object 2560 moves away from the light emitting device 2210, a driving method to gradually decrease the brightness of the light emitting device 2210, as the object 2560 moves away from the light emitting device 2210 may be implemented. The controller 2100 may reduce brightness of light emitting device 2210 by driving light emitting diode arrays including a successively smaller number of light emitting diodes as the object 2560 moves further away from the light emitting device 2210. The driving methods may be applied to all light emitting devices in an area. The driving methods may be applied to each light emitting device individually or by groups.

In the method to gradually increase the brightness of the light emitting device 2210, the controller 2100 may predict that the object 2560 will keep moving in a certain direction and increase the brightness of a light emitting device 2220 that is located adjacent to the light emitting device 2210 in the moving direction of the object 2560. The controller 2100 may predict the moving direction of the object 2560 and adjust the illumination state of the light emitting device located in the predicted moving direction.

FIG. 29 is a flowchart of an illumination method according to an exemplary embodiment of the present invention.

In operation S2910, an illumination state is set according to an initial state of the illumination system 2000.

In operation S2920, sensing information collected by sensors or the like is received. The sensing information processing unit 2216 may be included in each light emitting device and may receive the sensing information and may send the received sensing information to the controller 2100. The controller 2100 may directly receive the sensing information from the sensors. The sensing information may include brightness information of an area or motion information of an object moving in the area.

In operation S2930, based on the sensing information, the controller 2100 establishes groups each including one or more light emitting devices therein. In order to establish illumination state of the respective groups differently, the groups may be established based on the brightness information or the motion information of the object. Light emitting devices located in a bright area and light emitting devices located in a dark area may be separated into different groups. When the object is moving, light emitting devices adjacent to the object and light emitting device further from the object may be established into different groups.

In operation S2940, an illumination state of each group is adjusted. In the group located in a bright area, the illumination state of that group's light emitting devices may be adjusted to be relatively lower than the initial illumination state. In the group located adjacent to the object, the illumination state of that group's light emitting devices may be adjusted to increase the brightness thereof.

In operation S2950, the sensing information is received. In operation S2960, the controller 2100 determines whether the received sensing information changed, i.e., whether a state information of the area is changed. A change in the state information may include a decrease of the brightness of the area due to the darkening of the outside light, a change in the moving direction of an object, a change in the speed of an object, and the like.

If the state information has not changed, the prior illumination state is maintained, and the method returns to operation S2950 and operation S2960.

If the state information is changed, the method returns to operation S2930 and proceeds to operation S2940.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

1. An illumination system, comprising: a plurality of light emitting devices arranged in an area and spaced apart from each other, each light emitting device comprising a plurality of light emitting diode arrays each comprising one light emitting diode or a plurality of light emitting diodes connected in series, the numbers of light emitting diodes in each light emitting diode array being different from the number of light emitting diodes in each other light emitting diode array; and a controller configured to establish one or more groups, each group comprising one or more of the light emitting devices, and the controller is configured to adjust an illumination state of a selected group of the one or more groups by adjusting the illumination state of each light emitting device in the selected group by controlling a driving state of the light emitting diode arrays included in each light emitting device of the selected group, wherein the controller is configured to determine the number of light emitting devices included in each group based on sensing information.
 2. The illumination system of claim 1, further comprising a sensor configured to detect sensing information.
 3. The illumination system of claim 1, wherein the sensing information comprises at least one of brightness information of the area, brightness information of outside the area, speed information of an object, moving direction information of the object, time information, position information of the object, and position information of the light emitting devices.
 4. The illumination system of claim 1, wherein the controller comprises: a reception unit configured to receive sensing information; and a control signal generation unit configured to generate a control signal to control the driving state of the one or more the light emitting diodes in response to the sensing information.
 5. The illumination system of claim 1, wherein the controller is configured to sequentially adjust an illumination state of a group adjacent to the selected group.
 6. The illumination system of claim 5, wherein the controller is configured to drive, for each of the light emitting devices of the group adjacent to the selected group, a light emitting diode array comprising a smaller number of light emitting diodes than the number of light emitting diodes comprising the light emitting device of the selected group.
 7. The illumination system of claim 5, wherein the controller is configured to drive, for each of the light emitting devices of the group adjacent to the selected group, a light emitting diode array comprising a larger number of light emitting diodes than the number of light emitting diodes of the light emitting device of the selected group.
 8. The illumination system of claim 1, wherein the controller is configured to drive the same number of light emitting diode arrays in each light emitting device of the same group.
 9. The illumination system of claim 1, wherein the area is a space exposed to an external light source, the controller is configured to establish a first group comprising one or more light emitting devices located adjacent to the external light source and one or more additional groups each comprising one or more light emitting devices arranged farther from the external light source than the first group, and the brightness of the light emitting devices of the first group is lower than the brightness of the light emitting devices of the one or more additional groups.
 10. The illumination system of claim 9, wherein the controller is configured to adjust the brightness of the light emitting devices of the first group depending on the brightness of the external light source, the controller is configured to increase the brightness of the light emitting devices of the first group if the brightness of the external light source is lower than a first reference value, and the controller is configured to decrease the brightness of the light emitting devices of the first group if the brightness of the external light source is equal to or higher than the first reference value.
 11. The illumination system of claim 9, wherein the controller is configured to adjust the number of additional groups depending on the brightness of the external light source, the controller is configured to increase the number of the additional groups if the brightness of the external light source decreases, and the controller is configured to establish a brightness of the light emitting devices in each additional group.
 12. The illumination system of claim 1, wherein the area is a space comprising an entrance, an exit, and is elongated in a lengthwise direction, the controller is configured to establish a first group comprising a light emitting device located adjacent to the entrance of the area, a second group comprising a light emitting device arranged adjacent to the exit of the area and one or more additional groups each comprising a light emitting device arranged between the first group and the second group, and the brightness of the light emitting device in the first group and the light emitting device in the second group is lower than the brightness of the light emitting device of the one or more additional groups.
 13. The illumination system of claim 12, wherein the controller is configured to adjust the number of light emitting devices in the first group or the second group depending on a brightness of outside the area, if the brightness of the outside of the area is lower than a second reference value, the controller is configured to decrease the number of light emitting devices in the first group or the second group to below a first initial value, and if the brightness of the outside of the area is equal to or higher than the second reference value, the controller is configured to increase the number of light emitting devices in the first group or the second group to equal to or larger than the first initial value.
 14. The illumination system of claim 12, wherein the controller is configured to adjust the number of light emitting devices in the first group or the second group depending on the brightness of outside the area, if the brightness of outside the area is lower than a third reference value, the controller is configured to increase the brightness of the light emitting devices in the first group or the second group to be equal to or larger than a second initial value, and if the brightness of outside the area is equal to or higher than the third reference value, the controller is configured to decrease the brightness of the light emitting devices in the first group or the second group to below the second reference value.
 15. The illumination system of claim 12, wherein the controller is configured to adjust the number of the one or more additional groups depending on the brightness of the area, and the number of the one or more additional groups increases with an increase in a difference between the brightness of a first point and a second point in the area.
 16. The illumination system of claim 12, wherein the controller is configured to adjust the number of the one or more additional groups depending on a speed of an object that enters the entrance of the area, and the number of the one or more additional groups decreases as the speed of the object increases.
 17. The illumination system of claim 1, wherein the area is a space elongated in a lengthwise direction, the controller is configured to establish the one or more groups based on a distance between the one or more light emitting devices and an object, and the farther a group is located from the object, the smaller the number of light emitting diodes arranged in the light emitting diode array driven in each light emitting device of the group.
 18. The illumination system of claim 1, wherein the area is a space elongated in a lengthwise direction, in response to an object approaching the area, the controller is configured to establish a first group comprising one or more light emitting devices within a threshold distance from the object and a second group comprising one or more light emitting devices farther away from the object by a distance larger than the threshold distance, and the number of light emitting diodes driven in each light emitting device of the first group is larger than the number of light emitting diodes driven in each light emitting device of the second group.
 19. The illumination system of claim 18, wherein in response to the object moving away from the first group, the controller is configured to reduce the brightness of each light emitting device of the first group.
 20. A method of driving a plurality of light emitting devices in an area, the method comprising: driving a first light emitting diode array of the light emitting devices based on an initial illumination state; receiving sensing information for the area; dividing the area into a plurality of groups, each group comprising at least one light emitting device, based on the received sensing information; and adjusting an illumination state of the light emitting devices in each group in response to the sensing information.
 21. The method of claim 20, wherein adjusting the illumination state of the light emitting devices comprises: increasing the brightness of the light emitting devices by driving a second light emitting diode array comprising a larger number of light emitting diodes than the first light emitting diode array; or decreasing the brightness of the light emitting devices by driving a third light emitting diode array have a smaller number of light emitting diodes than the first light emitting diode array.
 22. The method of claim 20, wherein adjusting the illumination state of the light emitting devices comprises: adjusting the number of light emitting devices included in each group.
 23. The method of claim 20, further comprising: establishing a first group adjacent to an entrance of the area and a second group adjacent to an exit of the area, and a third group between the first group and the second group, and if a brightness outside the area is above a first reference value, adjusting the illumination state of the first group and second group to be lower than the illumination state of the third group.
 24. The method of claim 20, wherein the sensing information comprises at least one of brightness information of the area, brightness information of outside the area, speed information of an object, moving direction information of an object, time information, position information of the object, and position information of the light emitting devices. 